The invention relates to a method and a device for evaluating the quality of a yarn.
At present, several possible ways of evaluating the quality of a yarn are known.
A first possibility is to measure variations in the mass of the yarn over its length and to count and estimate the deviations from a mean value. For said purpose, the yarn may be scanned by an electric field or by a light beam.
A second possibility is to measure the tensile strength of a yarn using a tensile strength test. The behavior of the yarn during said tensile strength test again provides information about the quality of the yarn.
A third possibility is to measure the hairiness of the yarn, i.e. the length, number or frequency of fibers protruding from the body of the yarn.
All of the above possibilities and further possibilities not described here provide information about one or more properties of a yarn which are collectively conceived as the quality of the yarn. One of said properties, e.g. the mass variation,; relates to the appearance of the yarn or the textile fabric manufactured using said yarn. Another property, e.g. the tensile strength, relates more to the physical properties or to the behavior during further processing. A further property, e.g. the hairiness, relates more to the feel which the yarn imparts to the textile fabric when it is touched, and so on.
A drawback of the presently known methods and devices for evaluating the quality of a yarn is that they are unable to evaluate the quality as a whole. There are still aspects of the quality of a yarn which are not identified by the known methods and devices. Thus, yarns which according to certain criteria and properties have to be classified as good because they are very uniform and have a high tensile strength, for example, nevertheless cause problems during processing, e.g. during spooling, weaving etc., which limit the output of the respective processing stage.
The invention as characterized in the claims now achieves the object of providing a method and a device, with which further aspects of the quality of a yarn may be taken into consideration and explained by measured values so that the quality of a yarn as a whole is substantially detectable.
Said problem is solved in that, for evaluating the quality of a yarn, first measured values for at least one parameter of the yarn are acquired from a continuously moving yarn which is previously exposed to friction, that second measured values of the at least one parameter of the yarn are acquired from said yarn when the yarn is not previously exposed to friction and that the first and the second measured values are processed together to form third measured values which are a measure of the quality of the yarn. A device for effecting the method accordingly comprises at least one measuring head, a friction element and an evaluation unit for signals from the measuring head.
The advantages achieved thereby are that it is therefore possible to indicate a new measure of a property or quality of the yarn which is crucial for the output of the processing stages which are charged with yarn. In such processing stages yarn is, for example, drawn through elements and rubbed against elements. If the yarn stands up well to comparable loads in a test without altering substantially, then there is a high probability that it will also stand up well to further processing. This may be evaluated on the basis of measured values determined using the proposed method or the proposed device.